Conventionally, a driving device for semiconductor elements capable of coping with the possibility of damage to a semiconductor element caused by an excess current due to a short circuit, as disclosed in Japanese Patent Laid-Open No. 2002-208847 for example, is known. By detecting a collector current in a semiconductor element such as an IGBT, gate shutting for example, which is a protective operation at the time of detection of an excess current, is performed.
Detection of a collector current in a semiconductor element from a collector-emitter voltage VCE detected with a diode is performed. This collector current detection method is thought to be ineffective in accurately detecting the collector current from the VCE detection value in a time period of several microseconds from turn-on to entering a steady state. On the other hand, in a case where a load short circuit or the like occurs due to some cause, a large current (short circuit current) flows immediately after turning on of the semiconductor element. It is preferable to rapidly detect this and perform a protective operation.
A technique to make the collector-emitter voltage VCE converge rapidly on a saturation voltage when the gate is turned on in the above-described conventional art has been disclosed. “Saturation voltage” refers to a drop in voltage between the collector and the emitter electrode when dropping of the voltage between the collector electrode and the emitter electrode stops decreasing while the base current is increased. Rapid sensing of the collector current with VCE after turn-on is enabled thereby. As a result, early execution of a protective operation after turn-on is enabled.